1. Field of the Invention
The present invention relates to a novel porphyrin dimer or higher porphyrin polymer. The present invention also relates to a method of producing the same.
Further, the present invention relates to another porphyrin dimer and a porphyrin monomer which constitute the porphyrin polymer of the present invention.
The porphyrin polymer of the present invention is expected to function as an element for efficiently capturing and transferring light energy. It is contemplated that the porphyrin polymer of the present invention is applied to an artificial photosynthesis element and an organic solar battery. Porphyrin is also known to function as a light-induced electron transfer element. Therefore, it is expected that the porphyrin polymer of the present invention can be applied to a light/electron element of a molecular size.
2. Description of the Related Art
Porphyrin is a cyclic tetrapyrrole in which four pyrrole nucleuses are connected with four methine groups. As porphyrin has a large conjugated system including eighteen π electrons, it is expected that a porphyrin polymer can be used as a material of molecular wire or the like. Some examples of synthesizing a porphyrin polymer have been reported.
For example, Osuka of Kyoto University and Sugiura of Tokyo Metropolitan University have reported methods of extending a porphyrin polymer chain by way of covalent bonds (K. Sugiura, H. Tanaka, T. Matsumoto, T. Kawai, Y. Sakata, Chem. Lett. 1999, 1193; N. Aratani, A. Osuka, Y. H. Kim, D. H. Jeong, D. Kim, Angew. Chem. Int. Ed. 39, 1458 (2000); and A. Tsuda and A. Osuka, Science, 293, 79 (2001)). However, each of these methods requires a synthetic process with a very large number of steps, which is economically disadvantageous. Further, in these methods, a porphyrin polymer having up to hundreds of porphyrin units can hardly be synthesized.
The inventors of the present invention have already discovered that imidazolylporphyrin metal complexes form a coordinate bond with each other, between molecules, thereby forming a porphyrin dimer or a higher porphyrin polymer (refer to the following reaction formulae 1 and 2, and Y. Kobuke, H. Miyaji, J. Am. Chem. Soc. 1994, 116, 4111; K. Ogawa, Y. Kobuke, Angew. Chem. Int. Ed. 2000, 39, 4070; and Japanese Patent Application KOKAI Publication No. 2001-213883, which corresponds to U.S. Pat. No. 6,429,310B1, the entire contents of which are incorporated herein by reference, and Patent Application KOKAI Publication No. 2001-253883, the entire contents of which are incorporated herein by reference, which corresponds to U.S. Ser. No. 09/802,923, filed Mar. 12, 2001). Each of these porphyrin polymers functions as an energy-transferring element and thus is expected to be applicable to a molecular electronics element.

The unique and advantageous feature of a porphyrin polymer constituted of imidazolylporphyrin metal complexes as its constituting units lies in that the porphyrin polymer is self-organized only by mixing imidazolylporphyrin monomers in a non-polar solvent. Accordingly, the only material that is sufficient to synthesize porphyrin polymer is porphyrin monomers, which are the smallest constituting units (refer to the above-mentioned reaction formulae 1 and 2). As compared with the methods of Osuka and Sugiura in which a porphyrin polymer chain is extended by way of covalent bonds, this method requires a smaller number of synthesis steps, and thus is more economical. According to the method, it is actually possible to produce an extremely large metal complex polymer having a molecular weight of 500,000 or so, in which the metal complexes are regularly arranged. However, in this method, the porphyrin polymer extended by coordinate bonds tends to have the coordinate bond thereof cut in a polar solvent, and there arises a problem that the medium and environment applicable to the resulting porphyrin polymer are limited to non-polar ones. This limitation significantly restricts the scope of application of the porphyrin polymer (refer to the reaction indicated by the arrow showing the shift from right to left, of the above-mentioned reaction formula 1). Therefore, it has been desired to synthesize a stable porphyrin polymer in which the porphyrin polymer chain is extended by way of coordinate bonds, is firmly fixed and the coordinate bonds thereof are no longer cut after the polymer formation.